The project is directed towards an increase in our understanding of the structure and function of membranes using fluorescent probes to report on conditions within the membrane. Studies will be carried out on lipid bilayers, red cells and their ghosts, and vesicles prepared from red cell membranes containing only the transmembrane protein, Band 3. In one set of studies we will determine the thermodynamic parameters governing the distribution of small nonelectrolytes within membranes and at their interfaces. In a second set of experiments, we plan to use energy transfer to measure distances across the red cell membrane and to determine whether the membrane, or the Band 3 protein, changes in transverse dimensions when immersed in solutions of varying osmolality. The presence of "boundary lipid" in human red cell membranes with properties distinct from bulk lipid will be examined using trans-paranaric acid (PNA) which preferentially partitions into solid phases. The distribution of PNA can be determined from its fluorescence lifetime which is very sensitive to the fluidity of the PNA environment.